THE maintenance of a polarized cell surface requires vectorial transport of vesicles to the apical and the basolateral membrane domains1. Transport of newly synthesized apical proteins and trans-cytosis from the basolateral to the apical surface have been demonstrated to depend on microtubules2–9. In contrast, movement of membrane proteins to the basolateral surface has been claimed to occur by diffusion and to be microtubule- and actin-independent2'4'5'7'10–12. We have re-examined the role of… CONTINUE READING